Bone replacement part made of glass ionomer cement

ABSTRACT

Bone replacement parts consisting of glass ionomer cement are superior to those made of ceramics especially since they may easily be produced and machined using common grinding and milling tools. The required prosthesis part may therefore be formed of freshly mixed glass ionomer cement during the respective operation, or an industrially prefabricated formed body approximating the idealized shape of the bone part to be replaced may be adapted to the anatomic conditions given.

This application is a continuation of application Ser. No. 07/489,826,filed Mar. 9, 1990, now abandoned.

BACKGROUND OF THE INVENTION

Bone structures or bone parts in the human body may be destroyed due toinflammatory processes, malignant tumors or traumatic events; they maybe replaced by suitable prostheses. Apart from metals, which are used toreplace highly strained bone structures, ceramic prostheses serve forreplacing less strained bone structures, such as in the region of thehead. Ceramic materials are used in this region for reconstructing,e.g., parts of the auditory ossicle chain, of the auditory walls or evenof the jaw.

Prosthetic parts must be adapted to the given individual dimensions andconditions. This is difficult to be done with ceramic prostheses due totheir complicated workability. Consequently, dimensional adjustabilityis a chief requirement in the design of ceramic protheses, whereas givennatural anatomic conditions can take into account only to a minorextent. A single-piece middle ear prosthesis designed according to thisconcept is described, e.g., in German Patent Specification 2,905,183.

Heterologous bone grafts, which are equally employed, are not alwaysavailable and have proven to be problematic in view of possible HIVinfections.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide bone structures,specifically bone replacement parts, made of body-tolerated materialwhich are readily manufactured extracorporeally to the shape and size ofthe bone part to be replaced or fitted from prefabricated parts.

This object is met by a bone replacement part, which is made of anon-foamed glass ionomer cement.

The glass ionomer cement may specifically include the followingconstituents:

(a) a calcium and/or strontium aluminium fluorosilicate glass powdercontaining 20 to 60 wt-% SiO₂, to 50 wt-% Al₂ O₃,0 to 40 wt-% CaO, 0 to40 wt-% F, 0 to 10 wt-% Na₂ O and 0 to 10 wt-% P₂ O₅, with a minimum of1 wt-% CaO and/or SrO,

(b) a polycarboxylic acid having an average molecular weight of 1.000 to20.000, in a concentration of 5 to 50 wt-% related to constituent (a),

(c) water, and optionally

(d) tartaric acid as a chelate-former.

In a preferred embodiment, constituent (a) contains 25 to 50 wt-% SiO₂,10 to 40 wt-% Al₂ O₃, 0 to 35 wt-% CaO, 0 to 35 wt-% SrO, 5 to 30 wt-%F, 0 to 8 wt-% Na₂ O and 1 to 10 wt-% P₂ O₅, with a minimum of 10 wt-%CaO and/or SrO. Specifically preferred are contents of 25 to 45 wt-%SiO₂, 20 to 40 wt-% Al₂ O₃, 10 to 30 wt-% CaO, 10 to 30 wt-% F, 1 to 8wt-% Na₂ O and 1 to 10 wt-% P₂ O₅.

The bone replacement structures according to the invention consist of acompact, i.e. non-foamed, glass ionomer cement and are formed outsidethe body, which is in contrast to the conventional dental use of glassionomer cements. It is thus possible to shape the bone replacement partintra-operatively from freshly mixed glass ionomer cement, let it cureoutside the body and subsequently implant the cured part. According toan method, industrially prefabricated formed bodies having a shapeapproximating that of the bone structure to be replaced in an idealizingmanner may also be adapted to the anatomic conditions. In contrast toceramic material, no problems arise in finishing glass ionomer cementformed bodies by means of the usual cutting methods.

The replacement parts according to the invention may be readily obtainedby plastically deforming a mixed cement mass which will cure within afew minutes to form a rigid part and may then be machined mechanicallyby means of usual grinding or milling instruments. Moreover, the curedpart will chemically combine with the freshly mixed and still plasticcement so that replacement parts in accordance with the invention mayeasily be secured in situ. It as an advantage that glass ionomer cementscombine to form a chemical bond with the body's hard tissues such asbones.

Moreover, the replacement parts according to the invention are verybio-compatible or bio-active, i.e. they are not enclosed by connectivetissue. Instead, new bone growth is facilitated in direct bone contactdue to the presence of a replacement part according to the invention.

The easy formability and workability permits individual shaping so thatthe bone replacement structures are capable of reproducing therespective natural bone in an idealized shape.

The term "formed body" used in this specification will be understood toinclude also granulates which are implanted to fill a bone defect.

DESCRIPTION OF PREFERRED EMBODIMENTS

The bio-mimetic bone structures formed extra-corporeally from non-foamedglass ionomer cement in accordance with the invention are suited for thefollowing applications:

(1) Ear

Outer ear

auricular frame replacement

Middle ear

idealized incus

idealized malleus

idealized stapes

TORP (Total Ossicular Replacement Prosthesis)

PORP (Partial Ossicular Replacement Prosthesis)

crescent-shaped structure for reconstructing the tympanic frame

partial or total replacement of the posterior auditory conduit wall

utilization in mastoid obliterations (closure of the temporal bone).

(2) Lateral base of the cranium

Covering a defect of the middle and posterior cranial fossa.

(3) Cranium

Replacement in case of calotte defects.

(4) Frontobase

Reconstruction of bony frontobase defects inclusive of the posteriorwall of the frontal sinus and dural lesions.

(5) Replacement of cranial bones especially in

cranium base defects and

cranium dome defects

replacement of facial bone defects in the middle face, e.g. of the bonynose frame, frontal bone, frontal sinus wall, nasal septum, orita base,orita dome, and front wall of the maxillary sinus

general replacement of bone substance and stabilization of middle facebridges, with a possible combination with conventionally utilizedplates.

(6) Larynx

Implants for stabilizing and replacing the trachea and the larynx

(7) Jaw surgery

alveolar appendix

hard palate

replacement of jaw parts, particularly in the lower jaw

replacement of bone defects, for stabilization and osteosynthesis inLeFort fractures

as facial bone pads in plastic surgery

Glass ionomer cements substantially consist of the followingconstituents:

(a) a glass or metal oxide which forms, by acid decomposition, metalions causing cross-linkage of (b),

(b) a polymer poly acid, with the acid functions being sulphonic,phosphonic or carboxylic acids,

(c) water, and optionally

(d) a chelate-former.

In addition, stabilizers, disinfectants, pigments, X-ray contrast mediaand other fillers may be contained.

The glass ionomer cements are available as mixtures of glass and apolymer poly acid, on the one hand, and water, on the other hand, withthe chelate-former being optionally admixed to one of the twoconstituents. It is equally possible to dissolve the polymer poly acidin water, admix the optional chelate-former and mix this solution withthe glass.

In addition to glass powders containing calcium, magnesium or lanthanumas specified in German Offenlegungsschriften 2,061,513 and 3,248,357,and glass powders containing strontium according to Published EuropeanPatent Application 0,241,277, glass powders comprising other cations maybe employed. Calcium- and/or strontium-fluorosilicate glasses areprefered so that the aluminium fluorosilicate glass powders may comprisethe following constituents in addition to oxygen:

    ______________________________________                                        constituent  calculated as                                                                            weight percent                                        ______________________________________                                        Si           SiO.sub.2  20 to 60                                              Al           Al.sub.2 O.sub.3                                                                         10 to 50                                              Ca           CaO        0 to 40                                               Sr           SrO        0 to 40                                               F            F          1 to 40                                               Na           Na.sub.2 O 0 to 10                                               P            P.sub.2 O.sub.5                                                                          0 to 10                                               ______________________________________                                    

At least 1 wt-% CaO and/or SrO must be contained. Further, a total of 0to 20 wt-%, calculated as oxides, of B, Bi, Zn, Mg, Sn, Ti, Zr, La orother trivalent lanthanides, K, W, Ge as well as other additives may becontained which do not impair the properties and are physiologicallyharmless. The glasses may be made visible in X-rays by addition of 10 to20 wt-% of La₂ O₃.

The powder particles preferably consist of

    ______________________________________                                        Si as SiO.sub.2                                                                             25 to 50 wt %                                                   Al as Al.sub.2 O.sub.3                                                                      10 to 40 wt %                                                   Ca as CaO     0 to 35 wt %                                                    Sr as SrO     0 to 35 wt %                                                    F             5 to 30 wt %                                                    Na as Na.sub.2 O                                                                            0 to 8 wt %                                                     P as P.sub.2 O.sub.5                                                                        1 to 10 wt %                                                    ______________________________________                                    

At least 10 wt-% Ca (calculated as CaO) and/or Sr (calculated as SrO)must be contained. Further, 0 to 10 wt-% of B₂ O₃, Bi₂ O₃, ZnO, MgO,SnO₂, TiO₂, ZrO, La₂ O₃ or other oxides of trivalent lanthanides, K₂ O,WO₃, GeO₂ as well as other additives are possible which do not impairthe properties and are physiologically harmless.

Particularly preferred powders contain:

    ______________________________________                                        Si as SiO.sub.2     25 to 45 wt %                                             Al as Al.sub.2 O.sub.3                                                                            20 to 40 wt %                                             Ca as CaO           10 to 30 wt %                                             F                   10 to 30 wt %                                             Na as Na.sub.2 O     1 to 8 wt %                                              P as P.sub.2 O.sub.5                                                                               1 to 10 wt %                                             ______________________________________                                    

Examples of the preferred compositions are listed in the followingTABLE:

                  TABLE                                                           ______________________________________                                        (wt %)                                                                                   A    B          C      D                                           ______________________________________                                        Si as SiO.sub.2                                                                            35.0   27.6       29.0 45.4                                      Al as Al.sub.2 O.sub.3                                                                     30.4   26.0       25.1 35.0                                      Ca as CaO    14.9   28.8       24.6 10.1                                      F            17.7   17.0       23.0 10.3                                      Na as Na.sub.2 O                                                                            2.7    2.1        2.2  6.9                                      P as P.sub.2 O.sub.5                                                                        6.9    8.3        5.8  2.4                                      ______________________________________                                    

The glass powder particles utilized in accordance with the invention maybe calcium or strontium depleted at their surfaces, as described forcalcium in European Patent Application 0,023,013.

The glass powders employed in accordance with the invention have anaverage grain size (weight average) of at least 1 μm, preferably 3 μm atleast. The average grain size (weight average) is 1 to 20 μm, preferably3 to 15 μm, especially preferably 3 to 10 μm. The particles have amaximum grain size of 150 μm, preferably 100 μm, especially preferably60 μm. A not too narrow grain size distribution is favourable forattaining good mechanical properties, the distribution being obtained bymilling and removing the coarse parts by screening.

The polymer poly acids used as constituent (b) may be polycarboxylicacids, e.g. polymaleic acid, polyacrylic acid, polyitaconic acid as wellas mixtures thereof or copolymers, particularly the maleic-itaconic acidcopolymers and/or the acrylic-itaconic acid copolymers known fromEuropean Patent application 0,024,056 as known in the production ofglass ionomer cement powders. The average molecular weight of thepolycarboxylic acids used is more than 500. An average molecular weightis preferably between 1.000 and 20.000, the range of 3.000 to 10.000being especially preferred. The polycarboxylic acid is preferablyemployed in a concentration of 5 to 50 wt-% related to constituent (a).

Known chelate-forming additives (cf. German Offenlegungsschrift2,319,715) may be used as constituent (d) in the glass ionomer cement inaccordance with the invention. Tartaric acid is preferably employed as achelate-former.

EXAMPLE 1

250 parts by weight of a calcium aluminium fluorosilicate glass powderhaving the composition A of the above TABLE are mixed with 100 parts byweight of a solution consisting of 37 parts of a copolymer (1:1) ofacrylic acid and maleic acid, 9 parts tartaric acid and 54 parts water.

A bone structure for replacing a posterior auditory wall may be formedmanually from the pasty material thus obtained. The replacement part iscompletely cured after 10 minutes and may be applied in situ withfreshly mixed and still plastic cement.

The bone replacement will be incorporated with no problem three weeksafter the operation and there will be no gaps in the structure.

EXAMPLE 2

Formed bodies of 15 mm×20 mm×5 mm are produced from the material mixedaccording to Example 1 and implanted in the left tibia of a baboon. Theimplant does not differ from the bone material on X-ray images. Twoweeks later, marked bone formation activity at the implant edge appears,and after another four weeks, the implant has been completely surroundedby newly formed bone material and the spot does no longer differ fromthe surrounding bone material as.

EXAMPLE 3

An idealized auditory ossicle (incus) having a rounded shape as shown inthe attached drawing is produced from the mixed cement of Example 1.Rounded shapes are more bio-compatible than the sharp-edged bodies suchas formed of ceramics. The danger of perforating the tympanum isminimized; epithelial cells preferably grow over round shapes.

EXAMPLE 4

The formed body according to Example 2 is worked by means of millinginstruments common in ENT-surgery, and an idealized incus is formedthereof (cf. the drawing). It may easily be worked without causingcracks, chippings or fractures in the formed body.

What is claimed is:
 1. An implant for replacing defective bone parts,the implant having a predetermined shape, wherein the implant is shapedintraoperatively and finished by curing extracorporally, or is bothshaped and cured extracorporally, the implant being a non-foamed,non-porous, glass ionomer cement comprising:(a) an aluminumfluorosilicate glass which forms by acid decomposition, metal ionscausing cross-linking of (b), (b) a polymer containing acid groupsselected from the group consisting of sulphonic, phosphonic, andcarboxylic acid, and (c) water.
 2. The bone-replacement part of claim 1further comprising a chelate-former (d).
 3. The bone-replacement part ofclaim 1, which consists essentially of components (a), (b), and (c). 4.The bone replacement part of claim 1 wherein component (a) comprises aglass powder selected from the group consisting of the oxides ofcalcium, magnesium, lanthium, strontium, and mixtures of at least two ofthese metals.
 5. The bone replacement part of claim 4, wherein:(a)comprises an aluminum fluorosilicate glass powder selected from thegroup consisting of calcium and strontium containing20to 60 wt-% SiO₂,10 to 50 wt-% Al₂ O₃. 0 to 40 wt-% CaO, 0 to 40 wt-% SrO, 1 to 40 wt-%F, 0 to 10 wt-% Na₂ O, and 0 to 10 wt%-% P₂ O₅, with a minimum of 1 wt-%of CaO if said powder is said calcium aluminum fluorosilicate or with aminimum of 1 wt-% SrO if said powder is said strontium aluminumflurosilicate, and (b) comprises a polycarboxylic acid having an averagemolecular weight of more than 500 in a concentration of 5 to 50 wt-%related to constituent (a).
 6. The bone replacement part of claim 5,wherein component (a) comprises:25 to 50 wt-% SiO₂, 10 to 40 wt-% Al₂O₃, 0 to 35 wt-% CaO, 0 to 35 wt-% SrO, 5 to 30 wt-% F, 0 to 8 wt-% Na₂O, and 1 to 10 wt%-% P₂ O₅,with a minimum of 10 wt-% CaO if said powderis said calcium aluminum fluorosilicate or with a minimum of 10 wt-% SrOif said powder is said strontium aluminum fluorosilicate.
 7. The bonereplacement part of claim 6, wherein component (a) comprises:25 to 45wt-% SiO₂, 20 to 40 wt-% Al₂ O₃, 10 to 30 wt-% CaO, 10 to 30 wt-% F, 1to 8 wt-% Na₂ O, and 1 to 10 wt%-% P₂ O₅.
 8. The bone replacement partof claim 5, wherein the average grain size of the glass powder is 1 to20 μm and wherein the maximum grain size of the glass powder is 150 μm.9. The bone-replacement part of claim 8, wherein said average size is 3to 20 μm and wherein said maximum grain size is 60 μm.
 10. Thebone-replacement part of claim 5, wherein component (b) has an averagemolecular weight of 1,000 to 20,000.
 11. The bone-replacement part ofclaim 10, wherein said molecular weight is 3,000 to 10,000.
 12. Thebone-replacement part of claim 5, wherein component (b) is selected fromthe group consisting of polymaleic acid, polyacrylic acid, polyitaconicacid, maleic-itaconic acid copolymers, acrylic-itaconic acid copolymers,acrylic-maleic acid copolymers, and mixtures of at least two of thesepolymers.
 13. The bone replacement part of claim 5 further comprising anadditive selected from the group consisting of stabilizers,disinfectants, pigments, x-ray contrast media, fillers other than thepreviously recited additives, and mixtures of at least one theseadditives.
 14. The bone-replacement part of claim 5, further comprisingtartaric acid (d) as a chelate former.
 15. The bone-replacement part ofclaim 5, wherein component (a) further comprises 0 to 20 wt. % of oxidesof metals selected from the group consisting of B, Bi, Zn, Mg, Sm, Ti,Zr, La, trivalent lanthanides other than said Sm, K, W, Ge, and mixturesof at least one of these oxides.
 16. The bone-replacement part of claim5 wherein said component (a) comprises an admixture of said strontiumaluminum fluorosilicate and said calcium aluminum fluorosilicate. 17.The bone-replacement part of claim 5, which consists essentially ofcomponents (a), (b), and (c).